1. Field of the Invention
Field of the invention relates to a crash survivable seat utilizing a plurality of swivel mounted energy absorbers. Four of the energy absorbers constitute two pairs, one pair of which is high mounted and the other low mounted; each one of the said four utilizes a single layer coil of wire captured in an annular space between two concentric cylinders where the radial clearance between the concentric cylinders is dimensioned and toleranced so that the wire is squeezed to create the necessary friction force to roll when the two concentric cylinders are loaded with opposing forces. An intermediate pair of energy absorbers as disclosed in the above cross-referenced Patent Application, are also utilized and are two-stage energy absorbers having a load-stroke wave form designed to eliminate or substantially reduce oscillatory forces on the occupant and to eliminate rebound characteristics after complete stroking of the seat bucket. The improvement of the invention is the combination of the "notched" energy absorbers, mounted intermediately to the seat bucket and frame with the lower and upper pairs of absorbing devices thereby providing a force-stroke relationship that reduces the probability of injury to the occupant during arbitrary impact attitudes.
2. Description of the Prior Art
It is well known that the stroking capability of the single-axis seat during combined angle crashes may not be adequate to limit the acceleration levels on the occupant in the vertical direction. The forces accompanying the impact and accelerations that occur during rotary wing or fixed wing crashes are known to be injurious and oftentimes fatal to crew members in a combined horizontal, roll, and vertical impact configuration where a single axis energy attenuating seat system is being utilized. The single axis system inherently contains large bending moments during the energy attenuation cycle which give rise to inconsistent G loads experienced by the occupant during a vertical or combined angle crash which are usually in excess of the acceleration level the human body can withstand without injury or fatality occurring.
Since the human body is an elastic mass, it is subject to a phenomenon known as dynamic overshoot which occurs when a large shock force is applied to the human body. When the rapid acceleration and deceleration forces resulting from oscillatory motion above-referred to as dynamic overshoot of acceleration are experienced by the human body, the possibility of injury or fatality is greatly increased. It is therefore desirable to eliminate or substantially reduce the dynamic overshoot accelerations and decelerations to which the human body is subject during vertical or combined angle impacts of rotary or fixed wing aircraft. This can be accomplished by utilizing upper, intermediate, and lower pairs of energy absorbing devices which are attached to the carriage of the seat in a manner which permits tri-axis energy absorption of the seat during a vertical or combined angle impact. The intermediate pair of energy absorbers used in such a configuration incorporate a two stage energy absorption system thereby substantially minimizing and eliminating dynamic overshoot effects on the seat occupant.